The significance of the conch in Lord of The Flies is evident from the outset. Ralph and Piggy discover it and are able to summon the boys to order to the point that the boys are in awe of the conch - and the person holding it - at first anyway. "Let him be chief with the trumpet-thing."(ch 1) Hence, Jack, although accepting the fact that the conch represents some kind of authority, will resent the fact until he is able to get the better of it.
In chapter 2, Jack uses the conch to his advantage, acknowledging that " We're not savages. We're English..." In chapter 5, when there's talk of the Beast, Jack has his say, enjoying himself as he discounts the Beast but scares the littleuns even though he asserts that "If there were a beast I'd have seen it."
Jack steadily begins to assume some control as his hunters paint their faces and hunt and he has his "tribe." When Piggy and Ralph join him "to make sure nothing happens,"(ch 9) Jack enjoys his authority and when Ralph tries to assert his position as chief, Jack shows his contempt and scoffs because they did not bring the conch with them and besides, "the conch doesn't count at this end of the island- "Even though Ralph tries to argue Jack does not care.
After Simon's death, even Ralph realizes how ineffectual the conch and his authority are becoming. When Jack and his tribe attack the others, it is not the conch they want but Piggy's glasses so they can start a fire and cook meat from any animals they hunt. Taking Piggy's glasses puts Jack in a position of authority and "He was a chief now in truth."(ch 10)
When Piggy and Ralph confront Jack and his tribe, Jack and Ralph fight and even when Piggy holds the conch, Roger continues throwing stones. The conch is forgotten and Piggy is ineffectual as Ralph tries to rationalize and Jack yells until Ralph cannot be heard. When Piggy is is struck by the rock and killed and the conch "exploded into a thousand white fragments"(ch 11) Jack's response is to attack Ralph and declares his position- "I'm Chief!"